Rigid, hinged-lid packets of cigarettes are currently the most widely marketed, by being easy to produce and easy and practical to use, and by effectively protecting the cigarettes inside.
In addition to the above rigid, hinged-lid packets of cigarettes, rigid slide-open packets have been proposed comprising two partly separable containers, one inserted inside the other. In other words, a rigid, slide-open packet of cigarettes comprises an inner container, which houses a foil-wrapped group of cigarettes and is housed inside an outer container to slide, with respect to the outer container, between a closed configuration, in which the inner container is inserted inside the outer container, and an open configuration, in which the inner container is extracted from the outer container.
A rigid, hinged-lid, slide-open packet of cigarettes has also been proposed in which the inner container has a lid hinged to rotate between a closed position and an open position closing and opening an open top end. The inner container lid has a connecting tab connected at one end to the lid, and at the other end to the outer container, to ‘automatically’ rotate the lid (i.e. without the user having to touch the lid) as the inner container slides with respect to the outer container.
Like all standard packets of cigarettes, rigid, hinged-lid, slide-open packets of cigarettes are wrapped in an overwrap made of transparent heat-seal material and having a tear-off strip. To apply the overwrap to the packet of cigarettes, a sheet of wrapping material is first folded into a tube about the packet of cigarettes to form a tubular wrapping, which is stabilized by a longitudinal heat seal and has two open ends at the top wall of the lid and the bottom wall of the outer container; the two ends of the tubular wrapping are then folded to complete the overwrap, and the two folded ends are then stabilized by corresponding transverse heat seals.
Each heat seal is made by subjecting the superimposed portions of the sheet of wrapping material to a combination of heat (to heat the wrapping material locally to above melting temperature) and pressure (to press firmly together and join the superimposed portions of the sheet of wrapping material); and heat and pressure are applied jointly by pressing a hot heat-seal pad onto the superimposed portions of the sheet of wrapping material, which are thus ‘pinched’ between the pad and the underlying wall of the packet of cigarettes. The underlying wall of the packet of cigarettes thus acts as a ‘contrast member’ onto which the pressure exerted by the heat-seal pad is transmitted.
In a rigid, hinged-lid, slide-open packet of cigarettes, there is often a gap between the top wall of the lid and the top wall of the underlying wrapped group of cigarettes (i.e. the top wall of the lid is a given distance from the top wall of the underlying wrapped group of cigarettes); and, when the heat-seal pad is pressed onto the top wall of the lid to stabilize the corresponding folded end of the overwrap, the top wall of the lid (which does not have the support of the top wall of the underlying wrapped group of cigarettes, due to the gap between them) may not be strong enough to withstand the pressure exerted by the heat-seal pad without collapsing and deforming significantly. The FIG. 7 schematic shows collapse of the top wall 12 of a lid 6 under the pressure of a heat-seal pad 29.
Significant deformation of the top wall of the lid under the pressure exerted by the heat-seal pad has two negative effects: firstly, it may be at least partly permanent, and so result in unsightly creasing of the top wall of the lid; and, secondly, it may at least partly impair the effectiveness of the heat-seal pad, and so result in a poor-quality heat seal.